In optical transport networks, network nodes are needed, which can flexibly switch high amounts of high speed data signals between a large number of input and output ports. Today, optical interfaces are available for signal rates of up to 40 Gbit/s and interfaces for signal rates of 100 Gbit/s are in the pipeline. The overall traffic capacity large network nodes can handle today is in the range of up to few terabit per second. Such network nodes are based on high-speed electrical signal switching.
Given the ever growing traffic demand in core networks, it can be anticipated that in the future network nodes with again higher switching capacity will be needed. Network nodes that perform switching in the electrical domain will be limited in size in terms of floor space and power consumption. All-optical switch technology is under development, but currently, optical switches are not yet available that allow to switch 100 Gbit/s signals in STS-1 or packet granularity at least not for big switches, and will be quite costly once mature.